Fix realtime eBird priors for live GPS

[evandhoffman]

Summary

• pass a live date into Pi realtime eBird prior scoring so seasonal mode is active
• let explicit per-frame GPS coordinates override a configured fallback FIPS
• add regression coverage for live metadata scoring and GPS/FIPS precedence

Root Cause

The live realtime path passed phone GPS into MetadataPrior.apply(...) without a date, so seasonal priors returned uniform weights. Separately, MetadataPrior.resolve_region(...) always preferred default_fips, even when a caller supplied explicit GPS coordinates.

Closes #44.

Tests

• uv run pytest tests/test_metadata.py::TestMetadataPriorWithDb::test_explicit_gps_overrides_default_fips tests/test_metadata.py::TestMetadataPriorWithDb::test_explicit_gps_outside_supported_region_ignores_default_fips tests/test_realtime_video_upload.py::test_live_stream_metadata_prior_receives_date --no-cov
• uv run pytest tests/test_metadata.py tests/test_realtime_video_upload.py --no-cov
• uv run pytest --no-cov
• uv run ruff check
• uv run ruff format --check